A big bore 62t/61x 701 is the best bang for the buck and is a very hard hitting motor. There are lots of engine builders who can do this for you so you are not just limited to those two companies. Basically they just remove the stock sleeves, bore the cylinder to accept the big bore sleeves and enlarge/shape the transfer and boost ports (usually while the sleeves are out due to easier access) then install the big bore sleeves and finish porting the motor and blending the cylinder/sleeve seems since they dont line up perfectly. Anyone who has a big bore 62t/61x will tell you its a very hard hitting motor and in my opinion the best motor before you go with billet and powervalve cylinders.
you could either use your engine to build or you could just sell your engine to fund the new motor and buy complete from Jetmaniac and have the piece of mind that you are getting all new/rubuilt parts and basically have a new motor.